The present invention relates to a remote visual inspection system for certain areas of vessels which are not accessible for inspection by personnel. It particularly relates to the inspection of a storage arrangement wherein there is a primary vessel for containing a fluid and an outer vessel, generally referred to as the containment vessel, which surrounds the primary vessel to prevent loss of fluid in the event of a rupture or leak in the primary vessel.
There are many reasons why a primary vessel containing a fluid would be contained within a secondary containment vessel. For example, if the fluid is hazardous or dangerous to the environment, the secondary vessel acts to catch and retain the fluid in the event of a leak. In addition, when the primary vessel contains a fluid which is at an extreme temperature, for example, either a cryogenic fluid or a high temperature fluid such as would be found in a nuclear reactor, the space between the primary and secondary vessels acts to provide insulation and minimize the loss of heat from the primary vessel to the environment.
A nuclear reactor presents a particularly difficult inspection problem since the space between the two vessels is at a relatively high temperature, generally 200.degree. C. or more. In addition, the space between the primary and secondary vesels generally is maintained at a minimum. In the event of a rupture in the primary vessel, the fluid would drain into the area between the two vessels. This could create an extremely dangerous situation if the fluid level in the primary vessel became so low as to expose the reactor core. If the core were exposed, it would not receive sufficient convection coolant, with the result being fusion of the core. Thus, if the space between the two vessels is not maintained relatively small to prevent this possibility, the alternative is to maintain an extremely large inventory of coolant in the primary vessel.
To ensure continued safe operation of, for example, a nuclear reactor, periodic inspection at least of the primary vessel outer wall is required. While various methods have been proposed for inspection of the interior of vessels, very few systems or methods are known for inspecting the narrow annulus that generally exists between a primary vessel and a containment vessel, particularly at the operating temperatures encountered in a nuclear reactor.
In addition to being able to inspect the interior of such an annulus, it also is necessary to know at all times precisely where the visual inspection device is located in order to compare subsequent inspections with those made earlier when it was known that the structural integrity of the vessel was intact. Further, it generally is desired, particularly in the case of nuclear reactors, that there be no penetration in the containment vessel at any level below that of the uppermost portion of the reactor core, the reason for this being obvious in that any such penetration represents another potential failure point in the system.
Accordingly, it is an object of the present invention to provide a system which permits precise location of a remote visual inspection device for examining the annular space between a primary vessel and a containment vessel. It is another object of the invention to provide a remote visual inspection system which can withstand exposure to an extreme range of temperatures.